The present invention relates to a method and an apparatus of detecting physical quantities representative of magnetism and temperature as well as light and pressure and in particular to a motor system and other apparatus utilizing the above method and apparatus.
Detection of magnetism and temperature by means of a sensitive element such as a magnetoresistive element or a thermistor has hitherto been practiced widely.
Generally, the sensitive element has such a property that its internal resistance changes in accordance with the presence or absence or the magnitude of a physical quantity and therefore by determining the magnitude of the resistance, the physical quantity can be detected.
On the other hand, the sensitive element has generally a hysteresis by which the sensitive element presents different resistance values with application of the same physical quantity thereto depending on whether the physical quantity has changed increasingly or decreasingly before application of the same physical quantity. It is well known in the art that the detection value includes an error due to the hysteresis.
In addition, the sensing characteristic of the sensitive element has a "depression" called Barkhausen noise and a "depression" eventually takes place in an output signal based on the sensing characteristic (see FIG. 21).
The hysteresis and depression are of a phenomenon which generally develops in the sensitive element and is remarkable, especially, in magnetosensitive elements.
An invention of magnetoresistive element described in Japanese patent unexamined publication JP-A-58-56485 and an invention of yoke type thin film magnetic head described in Japanese patent unexamined publication JP-A-63-96713 are directed to elimination of the hysteresis and Barkhausen noise.
More particularly, the former patent publication describes that hysteresis and Barkhausen noise are eliminated by applying a bias magnetic field Hc to a magnetoresistive element and the later patent publication describes that a location where a Barkhausen noise is generated is shifted to outside the detection range by applying a bias field to a magnetoresistive element.
Conventionally, however, in detecting physical quantities, by means of the sensitive element as in the case of the above patent publications, technique has been employed which detects the resistance of the sensitive element per se to provide an electrical signal.
In the aforementioned prior arts, the bias field is applied to the magnetoresistive element to decrease the hysteresis and Barkhausen noise or to shift the location of generation of Barkhausen noise but as far as the magnetic field to be detected changes, it is difficult to completely eliminate the hysteresis and Barkhausen noise.
The use of magnetoresistive element, therefore, involves problems such that the magnetic field can not be detected accurately and when this magnetoresistive element is used as a sensor for detection of position and speed, detection of incorrect position and speed may result to impair control capability. Further, when an analog value of the output signal from the magnetoresistive element is used as a position signal, there arises a problem that if the analog signal is interfered with a noise, a considerable position error occurs.
In addition, when a constant bias field is applied to an MR (magnetoresistive) element to improve linearity, the linearity is improved effectively for the magnetic field to be detected being small. But for the magnetic field of interest being large, the linearity is hardly improved so that the magnitude of detectable field is limited.
These problems are due to the fact that the resistance of the sensitive element per se is measured to provide a detection signal. In other words, by the recent scientific technology, it is still difficult to manufacture sensitive elements without hysteresis.